Surgical needle and suture combinations are well known in the surgical arts. Surgical needles and sutures are a fundamental mainstay of surgical procedures and trauma repair. Surgical sutures are conventionally woven or braided from natural or synthetic polymeric materials including silk, polyesters, polydioxanone, polylactide, and the like. The sutures may also be constructed from a monofilament. The sutures may be bioabsorbable or nonabsorbable.
Surgical sutures are typically mounted to conventional surgical needles to create a needle and suture combination for use by the surgeon to approximate tissue, etc. A conventional surgical needle is typically an elongated, curved structure having a distal piercing tip and a proximal suture mounting section. The needles may optionally have cutting edges to assist in tissue penetration. The proximal suture mounting sections may have conventional blind boreholes or channels for receiving the end of a suture. One or both ends of a surgical suture may be mounted in the channel or borehole and secured therein in a conventional manner, including conventional mechanical swaging in which the suture mounting end of the surgical needle is partially compressed, as well as adhesives, cements, etc. Surgical needles are conventionally made from biocompatible materials, especially metals and metal alloys such as surgical grade stainless steels.
Early in the development of surgical needles, channels were used to attach suture to the needle. This was an improvement over needles having eyelets wherein a suture was threaded through the eyelet in the field. However, channels, when closed (i.e., swaged), create a bump (to a lesser or greater degree) in the distal portion of the channel. Such bumps may be undesirable to surgeons and other medical professionals since a bump may disrupt the smooth passage of the needle through tissue. This characteristic of channeled needles was eliminated with the introduction of mechanically drilled boreholes for suture mounting, however mechanical drilling can only be utilized for low strength alloys and large diameter holes. The relatively recent utilization of laser drilling was an important advancement in this art and addresses this issue as it allows small diameter boreholes to be drilled in small diameter wires, especially wires made from high strength alloys, which are currently off-limits for the most part to mechanical drilling due to technological limitations.
Drilled boreholes in surgical needles are particularly desirable since the profile of the needle body is not altered in the same manner as when a channel is punched into the proximal suture mounting end of the needle. A smooth profile is desirable to the surgeon since it is believed to reduce tissue trauma and to reduce the force required to pull the needle through tissue with a commensurate reduction in drag. Drilled boreholes in surgical needles may be produced in a number of conventional manners. Two conventional methods used to drill boreholes, as previously mentioned, include mechanical drilling and laser drilling.
There are distinct differences between mechanically drilled and laser drilled boreholes. Mechanically drilled boreholes are typically uniform and precise in shape and profile as they take on the shape of the drill. Mechanically drilled surgical needles are easily inspected using conventional plug gages (i.e., machined cylindrical members having a constant diameter or, optionally, tapering from proximal to distal). Although mechanical drilling will typically produce a borehole having relatively precise dimensions and a precise configuration, there are several disadvantages that may be associated with mechanical drilling. These include slow drilling speeds in an automated high speed manufacturing system, drill wear and life, the difficulty in manufacturing production grade drills for needles having fine wire sizes, increased costs, and the inability to drill small diameter holes in high strength alloys in small wire sizes
Although laser drilling overcomes these problems, laser drilled holes, on the other hand, pose several other unique problems, although certainly manageable, that have yet to be addressed. Laser drilled needles tend to have several issues associated with the use of a laser to drill a borehole. For example, in cases where the laser melts the material to form the hole, there is the potential for recast to form on the interior of the hole, and such recast may affect suture attachment. Other issues may include the consistency of the borehole profile and the smoothness of the borehole, as well as the possibility of blow-outs.
Laser drilling processes have been developed for drilling boreholes in surgical needles. Examples of such processes are included in the following U.S. patents and patent application, which are incorporated by reference: U.S. Pat. No. 6,018,860, 5,776,268, 5,701,656, 5,661,893, 5,644,834, 5,630,268, 5,539,973, 6,252,195, and US20050109741. Such laser drilling processes have many advantages, including adaptability for high speed manufacturing processes, efficiencies and cost, the ability to drill small holes in small wire diameters in substantially any material, and reduced maintenance.
Although laser drilling processes have all of these advantages, as previously mentioned the boreholes drilled by lasers typically do not have the same precise dimensional configuration as mechanically drilled boreholes. Laser drilling utilizes a conventional laser that emits a laser beam, which is typically tapered or Gaussian, in shape. This means that the bore hole drilled by the laser beam is typically tapered as it gets deeper. The laser beam used for drilling is engineered with respect to parameters such as energy level, pulse, waveform, etc., to produce a borehole having a desired configuration and characteristics including borehole depth, length, cross-section, and orientation about the longitudinal axis of the needle and about the center of the needle wire body, such that the laser drilled borehole is capable of sufficiently and effectively accepting an end of a surgical suture for mounting and affixation.
This is the result of the very nature of laser drilling wherein a high energy, pulsed laser beam essentially liquefies or vaporizes the target metal in the proximal, suture-mounting end of the needle upon which the beam is directed. In some laser drilling, the molten material will reform inconsistently within the hole; this reformed material is commonly called recast, as mentioned previously. The recast can create a non-uniform hole condition which may affect suture insertion and attachment.
In order to effectively affix or mount the end of a surgical suture in a laser-drilled borehole in a surgical needle, the borehole should have a substantially uniform diameter, similar to a bore hole produced in a mechanically drilled needle, albeit tapered as mentioned above. Similarly, the length of the borehole must have maximum and minimum dimensions. A length that is too long may weaken the needle, while too short may result in needle/suture separation. And, the borehole must be relatively centered about the longitudinal axis of the proximal end of the suture needle.
The present state of the art with respect to the measurement of the dimensions of laser-drilled boreholes is to use conventional mechanical pin gages, as is the conventional standard for mechanically drilled boreholes. The use of pin gages is typically a manual procedure wherein statistically significant quantities of needles are selected from lots of drilled needles, and the pin gages are manually inserted by an inspector into the drilled boreholes. The resulting data is recorded. There are several disadvantages associated with the use of mechanical pin gages. While pin gages are ideally suited for mechanically-drilled needles, they are not especially suitable for laser drilled needle manufacturing for several reasons. First of all, pin gages are not adapted for use in high speed manufacturing processes. Also, the pin gages used to measure very small diameter boreholes are expensive and difficult to manufacture, and for the finer diameters are easily damaged. In addition, the use of pin gages will not provide information with respect to the presence of re-cast. Pin gages can easily measure a mechanically-drilled borehole as it is cylindrical in nature and has a regular profile, but a laser drilled borehole in a surgical needle is not typically cylindrical in profile and may contain re-cast and varying diameters along the length of the borehole. Thus, a pin gage can only approximate the minor diameter measurement of a laser drilled borehole, and provides no other information with respect to other important parameters such as taper, length, degree of centeredness, irregularities, degree of skewing, etc. The presence of re-cast may cause a misrepresentation of the true minor diameter of the laser drilled hole. Further, as mentioned above, the pin gage measurements fail to address potential variants in the borehole profile. The use of a pin gage does not indicate the major diameter or provide a representation of the variation in the borehole profile. Therefore the only measurement a pin gage can provide is an indication of the smallest potential diameter of the borehole, without a value or determination of variations in diameter, profile, degree of skewedness, and other critical parameters.
Another disadvantage associated with the use of pin gages is that pin gages do not provide real time data that can be used to immediately adjust production-processing parameters. Statistical sampling of a batch of drilled needles may indicate that the boreholes are out of specification, requiring the destruction of an entire out-of-specification batch of needles. Other disadvantages include: pin gage wear, whether the gage is a minus or plus in tolerance with respect to the required borehole measurement, and acceptance of boreholes that meet the pin gage criteria, but have undetected internal geometries that inhibit, or preclude subsequent suture attachment. Pin gage measuring is a manual process and, consequently, is not a procedure that can keep pace with a high speed surgical needle manufacturing processes required in modern needle manufacturing processes and typically associated with laser drilling. Statistical sampling of laser drilled needles, although possible, if one were willing to accept any attendant disadvantages, is potentially prohibitive and it would not be possible to inspect a statistically relevant sample in real-time. Therefore it is typically necessary to use a reduced sample size, which may lead to false positives, possibly resulting in the destruction of laser drilled needles that, if inspected at acceptable levels, would not result in such a loss and the commensurate expense associated with the loss of a production batch of needles. Another disadvantage of pin gage inspection methods includes the possible acceptance of boreholes that meet the pin gage criteria, but have undetected defects, internal geometries or configurations that inhibit, or preclude subsequent effective suture insertion and attachment, possibly resulting in failures in the field.
As discussed above, the conventional means of measurement for drilled boreholes, i.e., plug gaging, does not work well with laser drilled holes because of the numerous attendant disadvantages. Given the inconsistent profile of a laser hole, plug gaging only can provide the user with an indication of the minor diameter of the inconsistent profile, but fails to provide a measure of the major diameter and/or the hole profile. This is a serious drawback, as variation on the hole profile and the differences between the minor and major hole diameters directly affects the ability to secure the suture to the needle. In mechanically drilled holes this is not a factor as the hole is a reflection of the drill geometry. Another drawback is that pin gaging is extremely time-consuming and only as accurate as the pin gage is manufactured and maintained. Unfortunately, there are no options available other than physical destruction, specifically, mechanically cross-sectioning a needle and examining the shape of the borehole, which is difficult, laborious, time consuming, and not cost-effective to do with a statistically significant sample size, and does not provide real time information which can be used to control production processes.
Therefore, there is a need in this art for novel methods of characterizing drilled boreholes in a high speed manufacturing environment and using such characterizations to adjust and control laser drilling and subsequent manufacturing processes. The significant benefit of which is to improve yields, product performance, and improve product consistency.